Process for continuous production of polyarylene sulfide

ABSTRACT

There is disclosed a process for continuously producing a polyarylene sulfide which comprises reacting a sulfur source with a dihalogenated aromatic compound in an aprotic organic solvent, characterized by maintaining the content of the dihalogenated aromatic compound in the polymerization liquid after the substantial completion of the polymerization reaction at 5 mg/g or higher. It is made possible by the process according to the present invention to efficiently produce the polyarylene sulfide which has a high molecular weight and is excellent in thermal stability.

TECHNICAL FIELD

[0001] The present invention relates to a process for producing apolyarylene sulfide. More particularly, it pertains to a process forcontinuously producing a polyarylene sulfide which has a high molecularweight and is excellent in thermal stability.

BACKGROUND ART

[0002] A polyarylene sulfide (hereinafter sometimes abbreviated to as“PAS”), especially polyphenylene sulfide (hereinafter sometimesabbreviated to as “PPS”) is known as an engineering plastic which isexcellent in mechanical strength and heat resistance and the like andwhich has good electrical characteristics and high rigidity. Thus it iswidely employed as a variety of materials such as electronic parts,electrical parts and mechanical parts. In particular, a molded articleof a resin composition composed of polyphenylene sulfide and aninorganic filler is employed for a variety of purposes of use.

[0003] With regard to a conventional process for the production of a PASby reacting a dihalogenated aromatic compound such as p-dichlorobenzenewith an alkali metal sulfide such as sodium sulfide and lithium sulfidein the an aprotic organic polar solvent such as N-methyl-2-pyrrolidone(NMP), a prescribed amount of water is added to the process, since thealkali metal sulfide is insoluble in a polar solvent. In this case, thealkali metal sulfide is dissolved in a polar solvent in the presence ofwater, and a part thereof is turned into an alkali metal hydrosulfide byhydrolysis. The alkali metal hydrosulfide thus formed suppresses theimprovement in the molecular weight of a PAS, turns a terminal of apolymer into —SH group, thereby having caused such problems as theproduction of a PAS having inferior thermal stability.

[0004] In order to solve the above-mentioned problems, there areproposed a method for imparting a high molecular weight to a PAS whichcomprises adding water to reactants, and thereafter carrying outpreliminary polymerization at a low temperature {refer to JapanesePatent Application Laid-Open No. 9228/1989 (Showa 64)}, a method whichcomprises carrying out preliminary polymerization by adding a smallamount of water to reactants so as to increase the conversion of analkali metal sulfide, and thereafter carrying out polycondensation byadding water to the reactants {refer to Japanese Patent ApplicationLaid-Open No. 7332/1986 (Showa 61)} and the like.

[0005] However, any and all of the aforesaid methods still remainunsatisfactory in regard to the obtainment of a PAS which has a highmolecular weight and is excellent in thermal stability.

DISCLOSURE OF THE INVENTION

[0006] The present invention has been made in the light of the problemsas mentioned above. An object of the present invention is to provide aprocess for continuously producing a PAS which has a high molecularweight and is excellent in thermal stability. Another object of thepresent invention is to provide a PAS which has a high molecular weightand is excellent in thermal stability and besides a composition of thePAS.

[0007] In view of the above-mentioned problems, intensive extensiveresearch and investigation were made by the present inventors. As aresult, it has been found that in the case of producing a PAS byreacting a dihalogenated aromatic compound with a sulfur source such asa metal sulfide in a polar solvent, the objects of the present inventioncan be achieved by performing polymerization reaction, while thedihalogenated aromatic compound is added to the reaction system in aspecific excess amount over the sulfur source, and keeping the contentof the dihalogenated aromatic compound in the polymerization liquidafter the completion of the polymerization reaction at a specificconcentration or higher.

[0008] Thus the present invention has been accomplished on the basis ofthe foregoing findings and information. Specifically, the gist andsummary of the present invention reside in a process for continuouslyproducing a polyarylene sulfide which comprises reacting a sulfur sourcewith a dihalogenated aromatic compound in an aprotic organic solvent,characterized by maintaining the content of the dihalogenated aromaticcompound in the polymerization liquid after the substantial completionof the polymerization reaction at 5 mg/g or higher.

THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION

[0009] In the following, more detailed description will be given of thepresent invention.

[0010] 1. The Process for Producing a PAS

[0011] The process for continuously producing a polyarylene sulfideaccording to the present invention comprises reacting a sulfur sourcewith a dihalogenated aromatic compound in an aprotic organic solvent,and is characterized by maintaining the content of the dihalogenatedaromatic compound in the polymerization liquid after the substantialcompletion of the polymerization reaction at 5 mg/g or higher.

[0012] (1) Starting Material Components

[0013] {circle over (1)} Dihalogenated Aromatic Compound

[0014] The dihalogenated aromatic compound which is used for theproduction process according to the present invention is exemplified bydihalogenated benzene such as p-dihalogenated benzene andm-dihalogenated benzene, alkyl-substituted dihalogenated benzene,cycloalkyl-substituted dihalogenated benzene and the like such as2,3-dihalogenated toluene; 2,5-dihalogenated toluene; 2,6-dihalogenatedtoluene; 3,4-dihalogenated toluene;2,5-dihalogenated xylene;1-ethyl-2,5-dihalogenated benzene; 1,2,4,5-tetramethyl-3,6-dihalogenatedbenzene; 1-n-hexyl-2,5-dihalogenated benzene; and1-cyclohexy-2,5-dihalogenated benzene, aryl-substituted dihalogenatedbenzene such as 1-phenyl-2,5-dihalogenated benzene;1-benzyl-2,5-dihalogenated benzene; and 1-p-toluyl-2,5-dihalogenatedbenzene, dihalobiphenyl such as 4,4′-dihalobiphenyl, dihalonaphthalenesuch as 1,4-dihalonaphthalene; 1,6-dihalonaphthalene; and2,6-dihalonaphthalene, and the like, of which p-dichlorobenzene isparticularly preferable.

[0015] {circle over (2)} Aprotic Organic Solvent

[0016] Examples of preferably usable aprotic organic solvent include ingeneral, organic polar solvents such as amide compounds, lactamcompounds, urea compounds, organosulfur compounds and cyclicorganophosphorus compounds, which can be used as single solvent or amixed solvent.

[0017] The above-mentioned amide compounds among the polar solvents areexemplified by N,N-dimethylformamide; N,N-diethylformamide;N,N-dimethylacetoamide; N,N-diethylacetoamide; N,N-dipropylacetoamide;N,N-dimethylbenzoic acid amide, etc.

[0018] The aforesaid lactam compounds are exemplified byN-alkyl-caprolactam such as caprolactam; N-methylcaprolactam;N-ethyl-caprolactam; N-isopropylcaprolactam; N-isobutylcaprolactam;N-n-propylcaprolactam; N-n-butylcaprolactam; andN-cyclohexylcaprolactam; N-methyl-2-pyrrolidone (NMP);N-ethyl-2-pyrrolidone; N-isopropyl-2-pyrrolidone;N-isobutyl-2-pyrrolidone; N-n-propyl-2-pyrrolidone;N-n-butyl-2-pyrrolidone;N-cyclohexyl-2-pyrrolidone;N-methyl-3-methyl-2-pyrrolidone;N-ethyl-3-methyl-2-pyrrolidone;N-methyl-3,4,5-trimethyl-2-pyrrolidone;N-methyl-2-piperidone; N-ethyl-2-piperilidone; N-isopropyl-2-piperidone;N-methyl-6-methyl-2-piperidone; N-methyl-3-ethyl-2-piperidone, etc.

[0019] The aforesaid urea compounds are exemplified by tetramethylurea;N,N′-dimethylethyleneurea; N,N′-dimethylpropyleneurea, etc.

[0020] The aforesaid organosulfur compounds are exemplified bydimethylsulfoxide; diethylsulfoxide; diphenylsulfone;1-methyl-1-oxosulfolane; 1-ethyl-1-oxosulfolane; 1-phenyl-1-oxosulfolaneetc.

[0021] The aforesaid cyclic organophosphorus compounds are exemplifiedby 1-methyl-1-oxophosfolane; 1-n-propyl-1-oxophosfolane;1-phenyl-1-oxophosfolane, etc.

[0022] Any of the above-exemplified aprotic organic polar solvent can beused alone or by mixing with at least one other or by mixing with asolvent which is not cited above to the extent that the object of thepresent invention is not impaired by the mixing.

[0023] Of the various aprotic organic polar solvents as exemplifiedabove are preferable N-alkylcaprolactam and N-alkylpyrrolidone, amongwhich N-methyl-2-pyrrolidone is particularly preferable.

[0024] {circle over (3)} Sulfur Source

[0025] There are mainly usable as a sulfur source, an metal sulfidetypified by an alkali metal compound such as sodium sulfise, lithiumsulfide and potassium sulfide. Any of the above-mentioned sulfur sourcesmay be used alone or in combination with at least one other of them, oran alkaline earth metal sulfide, or a sulfur source other thosementioned above.

[0026] {circle over (4)} A Phase Separation Agent

[0027] There are preferably usable as a phase separation agent, lithiumchloride, sodium acetate and a salt of an alkali metal such as lithium,water and the like, of which lithium chloride is preferably used inparticular.

[0028] {circle over (5)} Others

[0029] In the present invention, a comonomer, a branching agent, an endterminator and the like may be used in combination with theabove-mentioned dihalogenated aromatic compound. Examples of thecomonomer include 2,3-dichlorophenol; 2,3-dibromophenol;2,4-dichlorophenol; 2,4-dibromophenol; 2,5-dichlorophenol;2,5-dibromophenol; 2,4-dichloroaniline; 2,4-dibromoaniline;2,5-dichloroaniline;2,5-dibromoaniline;3,3-dichloro-4,4′-diaminobiphenyl;3,3-dibromo-4,4′-diaminobiphenyl; 3,3-dichloro-4,4′-dihydroxybiphenyl;3,3-dibromo-4,4′-dihydroxybiphenyl; di(3-chloro-4-amino)phenylmethane;m-dichlorobenzene; m-dibromobenzene; o-dichlorobenzene;o-dibromobenzene;4,4′-dichlorodiphenyl ether; and 4,4′-dichlorodiphenylsulfone.

[0030] Examples of the branching agent include 1,2,4-trichlorobenzene;1,3,5-trichlorobenzene;1,2,3-trichlorobenzene;2,5-dichloronitrobenzene;and2,4-dichloronitrobenzene.

[0031] Examples of the end terminator include chlorobenzene;bromobenzene; iodobenzene; p-chloronitrobenzene; o-chloronitrobenzene;p-chlorocyanobenzene; o-chlorocyanobenzene; and halogenated phenol suchas p-bromophenol; m-bromophenol; o-bromophenol; p-chlorophenol;m-chlorophenol; o-chlorophenol; p-fluorophenol; m-fluorophenol;o-fluorophenol; p-iodophenol; m-iodophenol; and o-iodophenol. Of theseare preferable p-bromophenol and p-chlorophenol.

[0032] (2) Production of PAS

[0033] {circle over (1)} Amount of Starting Raw Material to be Used

[0034] The process for producing a polyarylene sulfide according to thepresent invention is characterized by maintaining the content of thedihalogenated aromatic compound in the polymerization liquid after thesubstantial completion of the polymerization reaction at 5 mg/g orhigher, preferably in the range of 6 to 20 mg/g. By doing in thismanner, it is made possible to efficiently obtain a PAS which has a highmolecular weight and is excellent in thermal stability. By the term“after the substantial completion of the polymerization reaction” asused herein is meant the point of time when the polymerization procedurecomes to the end, that is, the point of time of the outlet of acontinuous polymerizer.

[0035] In the case of continuously producing a PAS in accordance withthe present invention by reacting a sulfur source with a dihalogenatedaromatic compound as principal starting raw material components, theamount of the starting raw material to be used can be determined so thatthe content of the dihalogenated aromatic compound in the polymerizationliquid after the substantial completion of the polymerization reactionfalls within the above-mentioned range.

[0036] Specifically, the amount of the dihalogenated aromatic compoundto be used is preferably at least 1.05 by molar ratio based on sulfursource, more preferably in the range of 1.06 to 1.20 by molar ratiobased thereon. The molar ratio, when departing from the aforesaid range,sometimes gives rise to incapability of assuring a PAS which has a highmolecular weight and is excellent in thermal stability.

[0037] In the case of using water, the amount thereof to be used ispreferably in the range of 0.05 to 4.0 by molar ratio based on sulfursource, more preferably in the range of 0.1 to 3.0 by molar ratio basedthereon. The molar ratio, when being less than 0.05, brings about a fearof insufficient reaction, whereas the molar ratio, when being more than4.0 causes a fear of incapability of assuring a PAS which has a highmolecular weight.

[0038] In order to accelerate the polymerization reaction in the presentinvention, a metal hydroxide such as an alkali metal compound and/orN-methylaminobutyric acid salt of a metal such as N-methylaminobutyricacid salt of an alkali metal may be added to the reaction system inaddition to the above-mentioned starting raw material. The amount of theadditive to be used is preferably in the range of 0.01 to 1.0 by molarratio based on a metal sulfide, more preferably in the range of 0.05 to0.8 by molar ratio based thereon.

[0039] {circle over (2)} Reaction Conditions

[0040] The above-mentioned polymerization reaction in the productionprocess according to the present invention may be carried out at atemperature in the range of 230 to 290° C., preferably 240 to 280° C.,more preferably 250 to 270° C. Prior to the polycondensation,preliminary polymerization can be put into practice at a temperature inthe range of 180 to 230° C., preferably 190 to 220° C., more preferably195 to 215° C. The reaction time of polycondensation is in the range of0.5 to 10 hours, preferably 1.0 to 10 hours, more preferably 1.5 to 10hours. The reaction time, when being less than 0.5 hour, gives rise to afear of insufficient reaction, thereby leading to an insufficientincrease in the molecular weight of PAS, whereas the reaction time, whenbeing more than 10 hours, is not so effective in particular as expected.

[0041] In the present invention, the number of stages that are usable inthe polymerization vessel, which is not specifically limited, may bemultistage wherein the temperature condition may be altered per stage.

[0042] The polymerization vessel and an agitational impeller that areused in the process according to the present invention are notspecifically limited, but the polymerization vessel is preferably of thetype well suited for complete mixing, and the agitational impeller ispreferably a large size impeller such as a Full zone impeller.

[0043] The polymerization solution obtained after the substantialpolymerization can be subjected to washing operation by adding waterthereto to the extent that the PAS is not solidified. The amount ofwater, which varies depending upon the amount and the temperature of thepolymerization solution, may be such an amount that the PAS is notsolidified nor precipitated by overcooling. It is preferable to usuallyagitate the content in a washing vessel so that the polymerizationsolution and water are sufficiently mixed with each other.

[0044] A washing solution is not specifically limited provided thatimpurities or byproducts which are stuck to the polymer do not exertadverse influence on the polymer by being dissolved in the washingsolution. Examples of the washing solution include methanol, acetone,benzene, toluene, water and NMP, of which water is preferable.

[0045] The polymerization solution after the completion of thepolymerization reaction is sent to a separation vessel, where thesolution is subjected to a separation procedure to separate it into apolymer phase and a solvent phase.

[0046] For the purpose of assuring more sufficient effect on washing andseparation, the steps of washing and separation are preferably repeatedoptional plural times.

[0047] In the present invention, since the polymer phase in which thesteps of washing and separation have been completed still contains asolvent, it is preferable to remove the solvent. The solvent removalmethod is not specifically limited, but may be in accordance with a wellknown solvent removal method which is used in the production of PAS, forinstance, a flashing method disclosed in Japanese Patent ApplicationLaid-Open No. 33878/1995 (Heisei 7).

[0048] The PAS in which the solvent removal procedure has been completedcan be taken out in a molten state or in the form of granule after beingsolidified by cooling using a proper cooling method. The cooling methodis exemplified by air cooling, water cooling, oil cooling and the like.

[0049] 2. Polyarylene Sulfide (PAS)

[0050] The PAS which is obtained by the process according to the presentinvention has a sufficiently high molecular weight, including aninherent viscosity [η] of at least 0.10, preferably at least 0.14, amelt index [MI] of 0 to 1000 g/10 minutes. Such a resin as describedabove, which is excellent in thermal stability, is usable for variouspurposes of use under severe conditions.

[0051] The above-mentioned inherent viscosity is measured with aUbbellohde viscometer for 0.4 g/deciliter solution of the polyarylenesulfide obtained by the foregoing process in a -chloronaphthalene at206° C.

[0052] In addition, as an evaluation method for thermal stability in thepresent invention, there is suitably usable a method which comprisesobserving the variation in the inherent viscosity [η] of PAS by usingthe mixture of PAS with NMP and maintaining the mixture at a hightemperature (265° C.) for 8 hours. In this case, the mixing ratio of PASto NMP is optional, but in order to enhance the reproducibility, theevaluation is made usually by blending each of them in a same amount(mass), for instance 2.5 g each. Moreover taking into consideration thesolubility of this kind of resin, it is convenient to express theinherent viscosity [η] by the value at 206° C.

[0053] The PAS which is obtained by the production process according tothe present invention is a polymer containing at least 70 mol % of therepeating unit, for instance, represented by the constitutional formula:Ar—S—, wherein Ar is an arylene group. Typical PAS among those are a PPScontaining at least 70 mol % of the repeating unit represented by theconstitutional formula (I) and a PPS containing at least 70 mol % of therepeating unit represented by the constitutional formula (II):

[0054] wherein R¹ is a substituent selected from an alkyl group having 1to 6 carbon atoms, an alkoxy group, a phenyl group, a metal salt of acarboxylic acid, an amino group, a nitro group or a halogen atom such asfluorine, chlorine or bromine; m is an integer of from 0 to 4; and n isan average degree of polymerization in the range of 10 to 200:

[0055] wherein n is as previously defined.

[0056] The production process according to the present invention iseffective for any type of known molecular structures of PAS including asubstantially linear molecular structure without branched or crosslinkedstructure and a molecular structure having branched or crosslinkedstructure, said structure being dependent upon the production processthereof. The PAS is exemplified by a homopolymer or copolymer containingas a repeating unit, at least 70 mol %, preferably at least 80 mol % ofpara-phenylene sulfide unit. Examples of the constitutional unit forcopolymerization include meta-phenylene sulfide unit, ortho-phenylenesulfide unit, p,p′-diphenyleneketone sulfide unit,p,p′-diphenylenesulfone sulfide unit, p,p′-biphenylene sulfide unit,p,p′-diphenylene ether sulfide unit, p,p′-diphenylenemethylene sulfideunit, p,p′-diphenylenecumenyl sulfide unit and naphthy sulfide unit.Further as an object of the polyarylene sulfide resin according to thepresent invention, there are included in addition to the polyarylenesulfide having a substantially linear structure, a branched orcrosslinked polyarylene sulfide in which a small amount of a monomerhaving at least three functional groups as a part of monomers ispolymerized and a blended polymer in which the polyarylene sulfide justcited is blended with the above-cited substantially linear polymer.

[0057] The PAS resin composition according to the present inventioncomprises 20 to 90% by weight, preferably 20 to 70% by weight, morepreferably 40 to 70% by weight of the PAS to be obtained in theabove-mentioned process and 80 to 10% by weight, preferably 80 to 30% byweight, more preferably 60 to 30% by weight of an inorganic filler.Examples of the inorganic filler include glass fiber, carbon fiber,aramid fiber, potassium titanate whisker, silicon carbide whisker, micaceramics fiber, wollastonite, mica, talc, silica, alumina, kaolin, clay,silica - alumina, carbon black, calcium carbonate, titanium oxide,lithium carbonate, molybdenum disulfide, graphite, iron oxide, glassbeads, calcium phosphate, calcium sulfate, magnesium carbonate,magnesium phosphate, silicon nitride and hydrotalcite. Any of theabove-cited fillers may be used alone or in combination with at leastone other. Of the above-cited fillers, glass fiber is particularlypreferable.

[0058] The glass fiber is not specifically limited, but may be selectedfor use from among alkali glass, low alkali glass and non-alkali glass.The fiber length is preferably 0.1 to 8 mm, more preferably 0.3 to 6 mm,and the fiber diameter is preferably 0.1 to 30 micrometer (μm), morepreferably 0.5 to 25 μm. The fiber length, when being less than 0.1 mm,leads to lowered reinforcing effect, whereas the length, when being morethan 8 mm, brings about a decrease in fluidity of the composition. Thefiber diameter, when being less than 0.1 μm, brings about a decrease influidity of the resin, whereas the diameter, when being more than 30 μm,leads to lowered strength of the composition. The configuration of theglass fiber is not specifically limited, but may be selected for usefrom a variety of forms such as roving, milled fiber and chopped strand.The glass fiber may be used alone or in combination with at least oneother.

[0059] In order to enhance the affinity for a resin, the glass fiber maybe subjected to a surface treatment with any of a silane based couplingagent of aminosilane base, epoxysilane base, vinylsilane base ormethacrylicsilane base, a titan ate based coupling agent oftetramethyl-orthotitanate or tetraethyl-orthotitanate, a chromiumcomplex compound and a boron compound.

[0060] The process for preparing the PAS resin composition according tothe present invention is not specifically limited. The composition canbe prepared by blending the PAS, an inorganic filler and an additive tobe used at need such as a silane based coupling agent, antioxidant, heatstabilizer, lubricant, plasticizer, electroconductivity imparting agent,coloring agent and pigment; mixing the components with one another bymeans of a tumbler blender, Henschel mixer or the like; and subjectingthe resultant mixture to melt kneading granulation by the use of asingle screw extruder or multi-screw extruder or by using a kneader,Banbury mixer or the like.

[0061] A molded article according to the present invention can beproduced from the above-described PAS resin composition by means of aninjection molding method, extrusion molding method or the like method.

[0062] It is made possible through the process for continuouslyproducing a polyarylene sulfide according to the present invention toobtain the polyarylene sulfide which has a high molecular weight and atthe same time, is excellent in thermal stability by maintaining thecontent of the dihalogenated aromatic compound in the polymerizationliquid after the substantial completion of the polymerization reactionat 5 mg/g or higher.

[0063] The PAS which is obtained by the production process according tothe present invention is preferably usable as materials for a variety ofmolded articles such as materials for films, fibers, mechanical parts,electrical parts, electronic parts and the like.

[0064] In what follows, the present invention will be described in moredetail with reference to working examples. Evaluations were made of thePDCB concentration, the inherent viscosity of PAS and the thermalstability thereof by the following procedures:

[0065] {Measurement of PDCB Concentration}

[0066] The PDCB concentration was determined by an internal standardmethod by the use of gas chromatography, wherein use was made ofchloroform as the diluting solvent and 1,2,4-TCB as the internalstandard.

[0067] {Evaluation Method for Thermal Stability}

[0068] A miniatured pressure tight cell which had an internal volume of10 milliliter (mL) and was made of stainless steel type SUS 316 wascharged with 2.5 g of PAS and 2.5 g of N-methyl-2-pyrrolidone (NMP), andwas hermetically sealed. The cell was heated in an oil bath to raise thetemperature thereof to 265° C., which was maintained for 8 hours.Thereafter the cell was taken out from the oil bath and cooled, and thenthe PAS was withdrawn from the cell, washed with water and dried. Thusthe inherent viscosity [η] of the dried PAS was measured by thefollowing procedure.

[0069] {Measurement of Inherent Viscosity}

[0070] A sample of the PAS in an amount of 0.04±0.001 g was dissolved in10 mL of α-chloronaphthalene at 235° C. within 15 minutes, andmeasurements were made of the viscosity of the resultant solution to bemeasured in a thermostat at 206° C. and the viscosity of theα-chloronaphthalene free from the PAS polymer to determine the relativeviscosity. The inherent viscosity [η] was calculated by the followingformula using the relative viscosity thus obtained.

[η](deciliter/g)=In (relative viscosity)/polymer concentration

EXAMPLE 1

[0071] Preliminary Polymerization

[0072] A 1 m³ titanium-made starting material synthesis vessel equippedwith a stirrer was charged with 633 kg of N-methyl-2-pyrrolidone(NMP)and 100 kg (2.38 kilomole) of lithium hydroxide (LiOH.H₂O), and theresultant mixture was heated to and kept at 140° C. The water containedin the lithium hydroxide as a starting material was removed by batchwisedistillation. Thereafter, 65 N-kiloliter of gaseous hydrogen sulfide wasblown into the mixture at a temperature kept at 130° C. to synthesizelithium hydrosulfide.

[0073] Subsequently, blowing of hydrogen sulfide was stopped, and thesynthesis vessel was again heated to raise the temperature up to 205° C.Accompanying the temperature rising, the water by-produced on blowinghydrogen sulfide was removed by batchwise distillation, while lithiumsulfide was produced from lithium hydrosulfide.

[0074] After the completion of the reaction, the reaction productcontained 1.08 kilomole of lithium sulfide and 0.214 kilomole of lithiumN-methl-4-aminobutyrate. In the condition of a temperature 205° C., thereaction product was added 168.3 kg (1.145 kilomole) ofp-dichlorobenzene (PDCB) and further 5.3 kg of pure water to proceedwith reaction at 210° C. for 3 hours. Then the reaction liquid wascooled to 60° C. or lower, and the resultant reaction mixture was takenout from the reactor into a 20 liter vessel. The conversion of the PDCBwas 85%.

[0075] Continuous Polymerization

[0076] A 10 liter autoclave equipped with a Full zone impeller wascharged with 855 g of lithium chloride as a phase separation agent and5145 g of NMP, and was heated to raise the temperature up to 260° C. Theabove-prepared prepolymer was preserved at 60° C. and was continuouslysupplied to the reactor at a flow rate of 33.3 g/minute by the use of agear pump.

[0077] On the other hand, about 150 to 200 g of the polymerizationmixture was withdrawn from the reactor through a withdrawing nozzleevery 5 minutes approx. so as to maintain a constant liquid level. Theprocedure was continued for 24 hours, when the withdrawn sample wasseparated into the polymer and polymerization liquid by means ofdecantation filtration. Then the concentration of PDCB in thepolymerization liquid was measured. The resultant polymer was washedtwice with hot water and further with acetone, and then in a vacuum wasdried at 120° C. for 12 hours to evaluate the inherent viscosity [η] andΔ 72 . The results are given in Table 1.

EXAMPLE 2

[0078] The procedure in Example 1 was repeated to obtain a PASpolymerization mixture except that the amount of p-dichlorobenzene(PDCB) to be used was altered from 168.3 kg (1.145 kilomole) to 171.4 kg(1.166 kilomole). The results of evaluation made in the same manner asin Example 1 are given in Table 1.

EXAMPLE 3

[0079] The procedure in Example 1 was repeated to obtain a PASpolymerization mixture except that the amount of p-dichlorobenzene(PDCB) to be used was altered from 168.3 kg (1.145 kilomole) to 174.6 kg(1.188 kilomole). The results of evaluation made in the same manner asin Example 1 are given in Table 1.

COMPARATIVE EXAMPLE 1

[0080] The procedure in Example 1 was repeated to obtain a PASpolymerization mixture except that the amount of p-dichlorobenzene(PDCB) to be used was altered from 168.3 kg (1.145 kilomole) to 162.0 kg(1.102 kilomole). The results of evaluation made in the same manner asin Example 1 are given in Table 1. TABLE 1 PDCB concentration (mg/g)[η](dl/g) Δ[η](dl/g) Example 1 6.5 0.31 0.03 Example 2 9.5 0.26 0.02Example 3 11.9 0.24 0 Comparative 4.1 0.26 0.18 Example 1

[0081] Industrial Applicability

[0082] A polyarylene sulfide is known as an engineering plastic which isexcellent in mechanical strength and heat resistance and the like andwhich has good electrical characteristics and high rigidity. Thus it iswidely employed as a variety of materials such as electronic parts,electrical parts and mechanical parts. In particular, a molded articleof a resin composition composed of polyphenylene sulfide and aninorganic filler can be employed for a variety of purposes of use.

1. A process for continuously producing a polyarylene sulfide whichcomprises reacting a sulfur source with a dihalogenated aromaticcompound in an aprotic organic solvent, characterized by maintaining thecontent of the dihalogenated aromatic compound in the polymerizationliquid after the substantial completion of the polymerization reactionat 5 mg/g or higher.
 2. The production process according to claim 1wherein the content of the dihalogenated aromatic compound in thepolymerization liquid after the substantial completion of thepolymerization reaction is maintained in the range of 6 to 20 mg /g. 3.The production process according to claim 1 wherein the dihalogenatedaromatic compound is used at a ratio of at least 1.05 expressed in termsof molar ratio of the dihalogenated aromatic compound/the sulfur sourceat the time of polymerization reaction.
 4. The production processaccording to claim 1 wherein the dihalogenated aromatic compound is usedat a ratio in the range of 1.06 to 1.20 expressed in terms of molarratio of the dihalogenated aromatic compound/the sulfur source at thetime of polymerization reaction.
 5. The production process according toclaim 1 wherein the polymerization reaction is put into practice in thepresence of a phase separation agent.
 6. The production processaccording to claim 1 wherein the polymerization reaction is put intopractice in the presence of water.
 7. The production process accordingto claim 1 wherein the polyarylene sulfide has an inherent viscosity [η]of at least 0.1.
 8. A polyarylene sulfide resin composition whichcomprises 20 to 90% by weight of the polyarylene sulfide which isproduced by the production process as set forth in any of claims 1 to 7,and 80 to 10% by weight of an inorganic filler.
 9. A molded articlewhich is produced by molding the polyarylene sulfide resin compositionas set forth in claim 8.